Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy.
Mix in the egg and vanilla extract until well combined.
Alternate adding the dry mixture and the buttermilk to the butter mixture, starting and ending with the flour mixture. Stir until just combined.
Gently fold in the mini chocolate chips.
Using a cookie scoop or tablespoon, drop dollops of the batter onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes or until the edges are set. Let them cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
In a medium bowl, beat the cream cheese and softened butter until smooth. Gradually add powdered sugar and beat until combined. Stir in vanilla extract, coconut, and pecans.
Once the cookies are completely cool, spread a generous amount of coconut-pecan filling on the flat side of one cookie and top with another cookie to form a sandwich.
For best flavor, chill the whoopie pies in the refrigerator for at least 30 minutes before serving.